In the corner bead for drywall construction art two types of beads have been commonly used, the "nail-on" type and the "tape-on" type. Nail-on beads commonly take the form of an angle strip of metal with side flanges meeting at a center corner rib providing shoulders against which spackle or joint cement can be dressed when feathered from the adjoining wall surfaces to cover the edges and outer faces of the side flanges and the heads of the nails securing these flanges to the wall structure. These nails are usually driven through the bead flanges at intervals of no more than eight inches.
Another form of nail-on bead has a rounded nose section between side flanges and presents step-down shoulders at the junctures of the rounded nose and the side flanges. The nails are driven through the side flanges and the spackle or joint cement covering the flanges is dressed to the shoulders, leaving the rounded nose section exposed to be painted later. For purposes of later discussion, corner beads with an abrupt corner will be referred to as the "hard-line" type, and the corner beads with a rounded nose will be referred to as the "soft-line" type.
Tape-on corner beads utilize paper wings to secure a metal corner angle in position rather than using nails. These wings are lateral extensions of a paper cover strip which is bonded by a hot melt glue or other suitable adhesive to the metal corner angle, usually on the outer faces of the side flanges. The metal corner angle can be shaped as the hard-line type or soft-line type. Spackle or joint cement and wall paint for dressing and finishing the corner, normally adhere significantly better to the paper cover strip of tape-on beads than to the exposed metal of nail-on beads. Also, normally drywall corners covered with nail-on heads are more susceptible to developing crack lines along the outer edges of the side flanges than when tape-on beads are used. On the other hand, nail-on beads have the advantage of requiring less skill to apply.
Preparatory to painting the wall board adjoining a corner covered by a corner bead, the spackle or joint cement spread from the wall surface onto the corner bead is sanded to provide a smooth continuous surface from the wall board to the corner bead. In the case of tape-on beads the exposed portion of the outer paper layer is commonly scuffed during the sanding operation, thereby making it more difficult to later obtain a smooth painted surface at the corner. This scuffing is usually most pronounced at the corner rib of a hard-lien bead, and at the two shoulders adjoining the rounded nose of a soft-line bead.